LOS ANGELES ― Bird flu was in decline, but health officials warned Monday that it appears to be on the rise again.

The United Nations Food and Agriculture Organization (FAO) “urged heightened readiness and surveillance against a possible major resurgence” of the virus, which has crossed over from birds to infect 565 people and kill 331 of them since its appearance in 2003.

At its peak in 2006, avian flu was present in 63 countries around the world. Just two years later, it was gone from most, and cases of illness in humans followed suit, dipping to just 302 in 2008. But almost 800 cases of bird flu were recorded in people during the last flu season, and the virus recently spread to Israel and the Palestinian territories, Bulgaria, Romania, Nepal and Mongolia, the FAO reported.

A 6-year-old girl in Cambodia died earlier this month after being infected with the virus, joining seven others in that country so far this year.

In people, H5N1 has caused symptoms including fever, cough, sore throat, muscle aches, eye infections, pneumonia, severe respiratory disease and, occasionally, death.

The cause of its reappearance now? Birds’ migrations, boosted by poultry farming practices, the FAO said. Also cause for concern: a new mutant strain of the virus, resistant to vaccines and known as H5N1 2.3.2.1, has been detected in China and Vietnam.

The FAO release noted that the countries where the disease has remained most active are the ones the most likely to suffer this flu season. These include Bangladesh, China, Egypt, India, Indonesia and Vietnam. Thus far, there have been no cases of H5N1 in people in the U.S., according to www.flu.gov, a website run by the U.S. Department of Health and Human Services.

But this flu can spread as easily as birds can fly ― and FAO chief veterinary officer Juan Lubroth warned that no country is completely safe. “This is no time for complacency,” he said, in the statement.

By Eryn Brown

(Los Angeles Times)

(McClatchy-Tribune Information Services)